In the decade since Sept. 11, 2001, the United States has developed an air force of drones to fight its new enemies. Faced with terrorists willing to take any life, we built machines that hunt and kill but donâ€™t bleed.

In the next decade, our reliance on drones and the spies who support them may increase for a different reason: Weâ€™re losing friends.

Since Sept. 11, the U.S. drone fleet has grown from a few dozen to 7,000. The Air Force now trains more pilots to operate drones than to fly bombers or fighter jets. Spy drones have flown extensively in Afghanistan and Iraq, where weâ€™ve fought ground wars. But killer drones have been particularly useful in Pakistan, where we canâ€™t send troops.

Every time U.S. ground forces have entered its territoryâ€”most recently in the raid that killed Osama Bin Ladenâ€”Pakistan has freaked out. But Pakistani leaders have tolerated U.S. drone strikes that killed nearly 2,000 insurgents in the countryâ€™s frontier provinces over the past five years. In fact, since the Bin Laden raid, the drone strikes have escalated and spread.

Hand in hand with the drone war, the CIAâ€™s role has expanded. Like the drones, the CIA is invisible. It can hunt and kill in a country without officially being there. So while the military operates our drones in Afghanistan, the CIA operates them in Pakistan. Apparently, weâ€™ve been allowed to launch some of our drone missions over Pakistan from bases within the country.

That may change. The Bin Laden raid, coupled with a lethal incident involving a U.S. agent inside Pakistan, has frayed the U.S.-Pakistan relationship. Instead of investigating Pakistani officials who may have helped shelter Bin Laden, Pakistan has rounded up people it suspects of helping the CIA set up the raid. Pakistan has also snuffed out a U.S. program to train Pakistani troops to fight al-Qaida. And the CIA has caught insurgents being tipped off when the U.S. shares intelligence with Pakistan.

So the U.S. is preparing to fight on without Pakistanâ€™s help. The backup plan is to move our drones to Afghan bases and fly them into Pakistan from there. And as we pull out of Afghanistan, weâ€™d leave drones in place. That way, we can continue to hunt al-Qaida in both countries even when, as a human presence, weâ€™re no longer there.

A similar scenario is unfolding in Yemen. With Bin Ladenâ€™s decline and death, al-Qaida in the Arabian Peninsula, led by radical cleric Anwar al-Awlaki, has become the chief orchestrator of terror plots against the U.S. The regime in Yemen, like the one in Pakistan, prefers that we fight this enemy with drones rather than ground forces.

Until now, the drone war in Yemen has been run by the U.S. military. But the military has screwed up. First it misidentified a target and killed a Yemeni envoy. Then it failed three times to take out Awlaki. But the bigger problem is that the Yemeni regime is unraveling. Its collaboration with U.S. forces has collapsed. Its political opponents want to take over and end U.S. military operations.

So the U.S. is preparing the same nonexit strategy. Weâ€™re putting extra CIA officers in Yemen and instructing the agency to run an expanded drone campaign based outside the country.

Legally, the U.S. military needs the consent of the host government to wage a drone war.* The CIA doesnâ€™t. The war can be euphemized as intelligence gathering and â€œcovert action.â€ Nor does Yemen have to host the drones. We can fly them over the border, as in Pakistan. We already launch drone missions over Yemen from Djibouti. Now, according to reports, weâ€™re building a CIA base outside Yemen from which we can run a drone war in that country without its approval. U.S. officials are keeping the baseâ€™s location secret, but the logical guess is Saudi Arabia, where the dronesâ€™ intelligence-gathering network will be headquartered. Presumably, the base will support a bigger drone fleet than the Djibouti airfield, where limited runway capacity has constrained the number of drone missions.

Weâ€™re also flying killer drones over Libya. But there, weâ€™re waging an open military conflict in concert with NATO. Whatâ€™s significant about Pakistan and Yemen is that theyâ€™re off the books. We use drones instead of ground troops. We donâ€™t even send pilots who can be shot down. We put the CIA in charge of the war so we donâ€™t have to respect the laws of war.* And we build bases outside the country so we can conduct the entire operation by remote control, except for the collection of targeting intelligence, which we leave to the CIA.

To top it off, we put the former director of the CIA, Leon Panetta, in charge of the military. And we put our top general, David Petraeus, in charge of the CIA. The CIA and the drones are the team of the future. Theyâ€™re the new face of a faceless war.

None of this is diabolical. Itâ€™s evolution. Al-Qaida, with its network of terrorist cells diffused among failed states, is an organism well-designed to evade conventional warfare. We, in turn, are evolving to fight the new threat. In a world of political chaos, waning American power, unstable allies, untrustworthy friends, and enemies who obey no rules, weâ€™re developing a new kind of war that we can wage from regional air bases with killer machines in the air fed by covert human networks on the ground. And the scary thing isnâ€™t that it might work. The scary thing is that it might not.

Clarification, June, 23, 2011: The Obama administration says that all its drone strikes respect the laws of war and that the U.S. military can legally wage a lethal drone campaign in a country without the consent of that countryâ€™s government. Specifically, State Department legal adviser Harold Koh said last year that it is the considered view of this Administration â€¦ that U.S. targeting practices, including lethal operations conducted with the use of unmanned aerial vehicles, comply with all applicable law, including the laws of war. â€¦

As a matter of international law, the United States is in an armed conflict with al-Qaida, as well as the Taliban and associated forces, in response to the horrific 9/11 attacks, and may use force consistent with its inherent right to self-defense under international law. â€¦

In this ongoing armed conflict, the United States has the authority under international law â€¦ to use force, including lethal force, to defend itself, including by targeting persons such as high-level al-Qaida leaders who are planning attacks. â€¦ [W]hether a particular individual will be targeted in a particular location will depend upon considerations specific to each case, including those related to the imminence of the threat, the sovereignty of the other states involved, and the willingness and ability of those states to suppress the threat the target poses.

On this view, when a state is unwilling or unable to deal with people within its borders who threaten the U.S., both the Department of Defense and the CIA can legally use drones or other lethal force against those people, in the name of self-defense, even without that stateâ€™s consent.